1. Field of the Invention
The present invention relates to a device for detecting a sighting direction of a driver in a vehicle from a remote place in a non-contact state.
2. Description of Related Art
It has been recently expected that such a driver's sighting direction detecting device is used as a non-contact human/machine interface for a vehicle in various fields, for example, to display visual information in a direction to which a driver turns his or her eyes, to operate a specific switch in accordance with a driver's sighting direction (direction of a driver's sight line), etc.
In order to achieve such a non-contact human/machine interface, a device in which a cornea reflected image of a driver is input and the driver's sighting direction is detected on the basis of position information of the cornea reflected image, has been hitherto proposed as a driver's sighting direction detecting device as described above. Here, the cornea reflected image is obtained when light irradiated to an eye-ball is reflected and refracted from each surface of an optical system constituting the eye-ball, and it is also called as "Purkinje's image".
As disclosed in Japanese Laid-open Patent application No. Hei-2-134130, this type of conventional sighting direction detecting device needs the following work: an cornea reflected image of a human being is picked up with a camera constituting a coaxial system with a light source, and the coordinate of reflected light of the light source is linked to the coordinate of the camera to obtain an equation for a line passing the center of a cornea ball and at the same time calculate the coordinate of the center of a pupil. In this conventional device, the above work is practically performed using two cameras which are disposed away from each other, and the driver's sighting direction is detected on the basis of the above coordinate information of the center of the cornea ball and the center of the pupil. That is, an intersection point between two lines each of which is obtained using each camera according to the above work is set as the center of the cornea ball, and a line which connects the coordinate of the center of the cornea ball and the coordinate of the center of the pupil is detected as a line of sight (sighting direction).
As described above, the conventional sighting directing detecting device as described above needs two cameras to detect the sighting direction, and thus its price is high.
In order to overcome this problem, the applicant of this application previously filed an application (Japanese Patent Application No. Hei-5-50619) on a line-of-sight measuring device having only one camera, so that the device can be designed at a low price. In this device, two illuminators which are disposed away from each other are alternately turned on at an extremely short time interval, and a pair of images (image pair) are picked up with the camera under illumination of the respective illuminators. On the basis of the image pair thus obtained, the coordinate value of a retina reflected image and the coordinate value of a cornea reflected image are calculated. A differential processing of the image pair thus obtained is performed for the calculation of the coordinate values of the retina reflected image and the cornea reflected image.
However, the device of the Japanese Patent Application No. Hei-5-50619 has the following problem. That is, when the differential processing is carried out with a TV camera using an ordinary NTSC signal, great positional deviation (displacement) may occur between the pair of images within a time interval between the times at which the respective images are taken into the device (picked up by the TV camera), due to vibration of a running vehicle, vibration of a driver which is caused by the vibration of the running vehicle or the like. In such cases, the positional deviation occurs in the coordinate value of the cornea reflected image, resulting in induction of a detection error. Therefore, this device has a disadvantage that the measurement (detection) of the sighting direction cannot be accurately performed.